1. Field of the Invention
The present invention relates to a refrigerant compressor for use in a vehicular air conditioning system. More particularly, it relates to a variable displacement compressor having an improved capacity control mechanism.
2. Description of Related Art
A known variable displacement compressor is described in Japanese Second (Examined) Patent Publication No. 3-13432. This compressor comprises a cylinder block having a plurality of cylinder bores radially formed therein and arranged about the central axis thereof, and a plurality of pistons slidably received in each of the cylinder bores, respectively. A front housing is securely fixed to a front end surface of the cylinder block to form a crank chamber therebetween, and a drive shaft extends axially through the crank chamber, such that the ends thereof are rotatably supported by the front housing and the cylinder block, respectively, through radial bearings. A conversion mechanism, which comprises shoes, a swash plate, the drive shaft, and the pistons, is provided on the drive shaft within the crank chamber for converting a rotating motion of the drive shaft into a reciprocating movement of the pistons. A hinge mechanism also is provided on the drive shaft within the crank chamber for supporting the swash plate at a variable tilt angle with respect to the central axis against the drive shaft. A cylinder head is fixed securely to a rear end surface of the cylinder block to form a suction chamber and a discharge chamber therebetween, and a valve plate assembly is provided between the cylinder block and the cylinder head. The known compressor has a capacity control mechanism for controlling pressure in the crank chamber. The tilt angle of the swash plate depends on the pressure in the crank chamber. When the tilt angle of the swash plate changes, the stroke or the length of the reciprocating movement of the pistons also changes, and, consequently, the capacity of compressed gas produced by the compressor changes.
The capacity control mechanism of this compressor, which is an outlet control-type mechanism, includes a control valve. The control valve includes a bellows and a needle valve. The bellows is disposed in a communication chamber, which communicates with the crank chamber via a communication passage. When pressure in the crank chamber is greater than the internal vacuum pressure of the bellows due to blow-by gas flowing from the cylinder bores, the needle valve opens the communication passage due to the collapse of the bellows. As a result, refrigerant gas in the crank chamber flows into the suction chamber, and the pressure in the crank chamber decreases. On the other hand, when pressure in the crank chamber is lower than the internal vacuum pressure of the bellows, the needle valve closes the communication passage because the bellows expands. As a result, the pressure in the crank chamber increases due to blow-by gas flowing from the cylinder bores. Thus, the capacity control mechanism controls the pressure in the crank chamber in order to change the tilt angle of the swash plate. As a result, the stroke of pistons is changed, and the volume of compressed gas produced is changed.
Another variable displacement compressor is described in Japanese First (Unexamined) Patent Publication No. 10-220347. This compressor has a capacity control mechanism, which is an inlet control-type mechanism. This compressor has a gas passage, which communicates between a discharge chamber and a crank chamber. The gas passage is controlled by a capacity control mechanism, which is disposed in a cylinder head.
In the outlet control-type, capacity control mechanism of the known compressor, however, when the discharge capacity of refrigerant gas is decreased its quantity by changing a suction pressure control point from low pressure to high pressure, blow-by gas flows into the crank chamber from cylinder bores. Pressure in the crank chamber increases, but is insufficient, because the increase is only due to blow-by gas from the cylinder bores. Therefore, it may be necessary to form another passage to communicate between the discharge chamber and the crank chamber to permit the introduction of refrigerant gas. Further, it may be necessary to form an orifice in this passage. As a result, the structure of this known compressor may be complicated.
In the inlet control-type, capacity control mechanism of the known compressor, however, the capacity control mechanism is disposed in the cylinder head. Therefore, when this known compressor is coupled with an engine of a vehicle, or when this known compressor is fitted with a coupling to an air-conditioning system, the flexibility in the equipment arrangement may be decreased due to the provision of the capacity control mechanism in the cylinder head.
An object of the present invention is to provide a variable displacement compressor, with the improved capacity response of an inlet control-type, capacity control mechanism.
Another object of the present invention is to provide a variable displacement compressor, which decreases manufacturing costs for the compressor without complicating its structure.
A further object of the present invention is to provide a variable displacement compressor, which increases the flexibility in the arrangement of the coupling for air-conditioning system.
In an embodiment of the present invention, a variable displacement compressor comprises a cylinder block having positioned therein a plurality of cylinder bores, a crank chamber, a valve plate, a suction chamber, and a discharge chamber, and a plurality of pistons, each of which is slidably disposed within one of the cylinder bores. A drive shaft is rotatably supported in the cylinder block. A swash plate is disposed in the crank chamber and is tiltably connected to the drive shaft. A hinge coupling mechanism is mounted on the drive shaft in the crank chamber for supporting the swash plate at a tilt angle with respect to the drive shaft. A coupling mechanism couples the swash plate to each of the pistons, so that the pistons are driven in a reciprocating motion within the cylinder bores upon rotation of the swash plate. A suction and discharge mechanism is connected to the valve plate for drawing refrigerant gas from the suction chamber into the cylinder bores and discharging the refrigerant gas from the cylinder bores to the discharge chamber. A communication passage communicates between the discharge chamber and the crank chamber. A capacity control mechanism is disposed in the communication passage for controlling the tilt angle by regulating a flow of refrigerant gas from the discharge chamber to the crank chamber. The capacity control mechanism is disposed along the a central axis of the compressor that corresponds to a line extension of the drive shaft. A first end portion of the capacity control mechanism projects into the discharge chamber. The first end portion of the capacity control mechanism has a screw mechanism for fixing the suction and discharge mechanism to the valve plate.
Other objects, features, and advantages will be apparent to persons of ordinary skill in the art from the following description of the invention with reference to the accompanying drawings.